1. Field of the Invention
The present invention relates to an improved seal structure for an end part of a liquid separation tube.
2. Description of the Prior Art
A reverse osmotic separation membrane or an ultrafiltration membrane is often used for recovering or separating solvents or solutes by separating the solvents from a feed solution, thereby to increase the concentration of the solutes in the feed solution. In these operations, a tubular membrane separation apparatus of the type wherein the feed solution is passed through the apparatus under pressure has been used as the separating means. In the case of reverse osmotic separation, for example, a pressure of 60 kgf/cm.sup.2 is commonly encountered.
In the tubular membrane separation apparatus of this type, a plurality of separation tubes are used with each separation tube having a mechanically strong porous support tube such as a perforated stainless steel tube or a porous FRP tube lined with a tubular membrane. The separation tubes are arranged in parallel and both ends of the separation tubes are fitted with coupling members so that the separation tubes communicate in series or in parallel. Thus, when a feed solution is allowed to pass through the separation tubes under a prescribed pressure, the solvent in the feed solution permeates through the tubular membrane of the separation tubes to flow from the porous support tube, thereby increasing the concentration of the solutes in the feed solution.
In order to interconnect the separation tubes to the input and output apparatus, a seal structure for the ends of the tubes capable of withstanding a high pressure is required. A typical seal of the prior art is shown in U.S. Pat. No. 3,480,147. Such a seal structure is demonstrated in FIGS. 1A and 1B. FIG. 1B shows a packing P' having an annular projection 12' molded on an end of a tubular part 1' having annular projections 11'. As shown in FIG. 1A, the tubular part 1' of the packing P' is inserted into an end part 2' of the separation tube and a tubular adapter 3' having an outside diameter somewhat larger than the inside diameter of the packing P' is then pressed into the packing P' so that the annular projection 12' of the packing P' is pressed against an inside circumferential wall 41' of a passage of the coupling member 4' and the projections 11' are compressed against the interior of the separation tube.
In this seal structure, adapter 3' is required to be thick for insuring close contact between the annular projections 11' at the tubular part 1' of the packing P' and the membrane 21' of the separation tube to produce the desired compressions therebetween as well as for insuring close contact and the desired compression between the annular projection 12' of the packing P' and the inside circumferential wall 41' of the passage of the coupling member pressure. The adapter 3' must also prevent the end part 13' of the tubular part of the packing P' from turning up when a cleaning ball is inserted into the separation tube to remove solid materials attached to the membrane of the separation tube.
In the case of reverse osmotic separation the adapter must be capable of withstanding very high pressure; therefore, it is necessary to remarkably increase the compression ratio of the packing. In addition, the outside diameter of the adapter is required to be rather large as compared with the inside diameter of the packing and the thickness of the adapter is also required to be large in order to withstand a compression stress of the packing. Consequently, the inside diameter of the adapter is small, which results in a large pressure loss as the feed solution passes therethrough. In addition, inserting the adapter into the packing is also difficult. These disadvantages become more severe as the pressure of the feed solution to be processed is increased. Furthermore, since the packing is compressed at a high compression ratio, when the separation apparatus is not operated the packing easily fractures due to fatigue at an early stage of its use.